What differentiates an optional referendum from a mandatory referendum?

An optional referendum is characterized by the ability of state legislatures to decide whether or not to place a measure on the ballot. This means that the legislature has the discretion to put a proposed law or policy change before voters for approval or rejection. In contrast, a mandatory referendum requires certain types of legislation or constitutional amendments to be voted on by the public regardless of legislative intent.

In this context, the distinction made in the correct choice highlights the role of state lawmakers in influencing which issues get presented to voters. This flexibility allows legislatures to assess public interest and political feasibility before committing to a referendum process. The other options do not accurately describe this key feature of optional versus mandatory referendums, focusing instead on control over the ballot process, requirements for voter initiation, or applicability to federal elections, which do not pertain to the differentiating factor between optional and mandatory referendums.